One area of concern to sensor array manufacturers is that of ensuring that the active area of their respective products (the pixel) covers the maximum amount of area such that there are substantially no gaps or minimal gaps between pixels. This amount of coverage is usually described as a percentage “fill-factor” and is computed as follows: fill-factor %=(pixel-pixel area)/(pixel active area)*100. In general, it is very difficult to achieve 100% fill-factor, and in some cases, the array process generally does not allow a large fill-factor such as is the case with CMOS sensor technology, for example. There are two primary reasons for achieving the goal of a high fill-factor which include:
1) To facilitate that a majority photons incident on the array are captured by the active parts of the array (i.e., increase sensitivity), and,
2) To facilitate that small structures in an image as presented to the array are not “lost in the spaces between pixels” whereby photons correlated with small structures are thus not captured by the active part of the pixel.
Some manufacturers have attempted to achieve a large effective fill-factor by the application of arrays of lenslets to the surface of the sensor array. This approach has the advantage of increasing the effective fill-factor and the sensitivity of the array, but suffers from chromatic effects. Also, lenslet processes by nature pose numerous difficulties in precise manufacture of micron-sized lenslets, and the associated problems in precise positioning. Therefore, lenslet style solutions add significant cost to the overall production of sensor arrays.